Which of the following statements is the first step in the synthesis and secretion of T3 and T4?
Synthesis of thyroglobulin by the follicular cells
Oxidation of iodide by the follicular cells
Coupling of T1 and T2
lodide trapping by the follicular cells
The Correct Answer is D
a) Synthesis of thyroglobulin by the follicular cells: This occurs after iodide has been trapped and transported into the follicular lumen.
b) Oxidation of iodide by the follicular cells: This is a later step; iodide must first be trapped before it can be oxidized into iodine.
c) Coupling of T1 and T2: This is one of the final steps in T₃/T₄ synthesis where iodinated tyrosines are joined.
d) lodide trapping by the follicular cells
Iodide trapping is the first step, where follicular cells actively transport iodide from the bloodstream into the thyroid follicle using sodium-iodide symporters.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
a) Stimulates the formation of white blood cells: This is associated with bone marrow and not parathyroid hormone (PTH).
b) Parathyroid hormone (PTH) increases blood calcium levels by stimulating bone resorption, increasing calcium reabsorption in the kidneys, and activating vitamin D to increase calcium absorption from the gut.
c) Increases the level of sodium ions in the blood: Aldosterone regulates sodium levels, not PTH.
d) Increases the level of potassium ions in the blood: This is also regulated by aldosterone and the kidneys, not PTH.
e) Increases the level of glucose in the blood: Glucagon and cortisol are more directly involved in increasing blood glucose.
Correct Answer is B
Explanation
a) On the inside of the plasma membrane: Catecholamines cannot cross the lipid bilayer, so they cannot bind to internal membrane receptors.
b) On the outside of the plasma membrane: Because catecholamines are water-soluble, they bind to extracellular receptors that initiate a second messenger cascade (e.g., cAMP).
c) In the cell cytoplasm: Only lipid-soluble hormones, like steroids, bind to intracellular receptors.
d) In the cell nucleus: Again, only lipid-soluble hormones (like thyroid hormones or steroids) reach nuclear receptors.
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